The preparation of dithiols derivatized with dithiocarbamic acids is known in principle (cf., for example, DE-A 22 56 511 and EP-A 530 590).
DE-A 22 56 511 discloses, inter alia, the synthesis of dithiols derivatized with dithiocarbamic acids via Bunte salts. On page 39, 3rd paragraph, such a synthesis is described using the example of the compound 1,4-bis(hexahydro-1H-azepin-1-ylthiocarbonyl-dithio)-2-butene as follows: 0.1 mol of 1,4-dichlorobutene-2 is reacted at boiling temperature with sodium thiosulphate pentahydrate in aqueous ethanol and the ethanol is subsequently removed by distillation. Further water, 0.3 mol of sodium acetate trihydrate and approx. 0.23 mol of formaldehyde are then added to the aqueous Bunte salt solution. An aqueous solution of sodium hexahydro-1H-azepin-1-ylthiocarbothiolate is then added dropwise at room temperature to this mixture over 0.5 h and the mixture is stirred at room temperature for a further 1.5 h. An organic solvent is not present in the reaction. The oily reaction product is extracted with chloroform at the end of the reaction, and the organic phase is washed with water and dried over anhydrous sodium sulphate. To obtain the 1,4-bis(hexahydro-1H-azepin-1-ylthiocarbonyldithio)-2-butene, the chloroform is evaporated. One disadvantage of this process is the high wastewater pollution by sodium acetate, i.e. owing to the high concentration of sodium acetate, the wastewater has a high chemical oxygen demand (COD). Thus, in the aforementioned example, at the reported yield of 71%, approx. 4.2 mol of sodium acetate are used for 1 mol of prepared product, which constitutes a very unfavourable ratio from an ecological point of view. In the reworking of the general information of DE-A 22 56 511 starting from 1,6-dichlorohexane in relation to the inventive compounds of the formula (I), which are illustrated in detail below, products which were difficult to filter and difficult to wash were additionally obtained in insufficient yield and sometimes insufficient purity (active substance content) (cf. Examples 17 and 18).
With regard to the preparation of dithiols derivatized with dithiocarbamic acids, EP-A 530 590 makes reference, for example, to EP-A 432 417. EP-A 432 417 discloses, as a synthetic route for the preparation of dithiols derivatized with dibenzyldithiocarbamic acid, in a very general manner, the reaction of 1,2-dichloroethane with sodium thiosulphate in aqueous solution and subsequent reaction of the resulting bis-Bunte salt with sodium dibenzyldithiocarbamate (page 4, lines 50 to 56). No remarks are made on reaction parameters to be employed advantageously. Nor are any working examples for the synthesis cited. In-house experiments on the reworking of the general synthesis information of EP-A 432 417 using the example of 1,6-dichlorohexane with regard to the inventive compounds of the formula (I), which are illustrated in detail below, have given rise to products which are difficult to filter and difficult to wash in insufficient yield and sometimes also insufficient purity (active substance content) (cf. Examples 19 and 20).
There is no description of any industrially simple, environmentally friendly and readily practicable preparation process which affords the inventive compounds of the formula (I) in high yields and in high purities.